Relation between serum sodium levels and prognosis in outpatients with chronic heart failure

INTRODUCTION: The predictive role of hyponatremia has been tested in acute and chronic heart failure. Sodium level is inversely related with renin-angiotensin-aldersterone system (RAAS) and sympathetic nervous activity but important issues remain unresolved. Our aim was to define the level of hyponatremia able to predict 1-year outcomes and investigate the relation between sodium levels and mortality and the effect of beta-blockers and angiotensin-converting enzyme (ACE) inhibitors on this relation. METHODS: We analyzed 4670 patients enrolled in the IN-CHF Italian Registry. We controlled the predictivity of hyponatremia, testing it either as a continuous variable and dividing the study sample into three severity groups: group 1 (≥136 mEq/l; n = 4207), group 2 (131-135 mEq/l; n = 389) and group 3 (≤130 mEq/l; n = 74). The linearity of the relationship between sodium levels and mortality was also tested. RESULTS: Mild-to-moderate and severe hyponatremia (groups 2 and 3) independently predicted the 1-year mortality. The relation between sodium concentration and death was not linear and a decrease of 1 mEq/l of sodium increased death rate only for values of sodium 142.9 mEq/l or less. This relationship was not modified by beta-blocker and ACE inhibitor therapies. CONCLUSION: Our data confirm the negative prognostic value of hyponatremia, even of moderate degree, independently of the use of recommended treatments for heart failure.